Speech communication critically depends on the capacity to produce the large set of sounds that compose a given language. The wide range of spoken sounds results from highly flexible configurations of the vocal tract, which filters sound produced at the larynx via precisely coordinated movements of the lips, jaw and tongue. Each articulator has extensive degrees of freedom, allowing a large number of different realizations for speech movements. How humans exert such exquisite control in the setting of highly variable movement possibilities is a central unanswered question.
The cortical control of articulation is primarily mediated by the ventral half of the lateral sensorimotor (Rolandic) cortex (ventral sensorimotor cortex, vSMC), which provides corticobulbar projections to and afferent innervation from the face and vocal tract. The U-shaped vSMC is composed of the pre- and post-central gyri (Brodmann areas 1, 2, 3, 6b), and the gyral area directly ventral to the termination of the central sulcus called the guenon (Brodmann area 43). Using electrical stimulation, the somatotopic organization of face and mouth representations in human vSMC has been described. However, focal stimulation could not evoke meaningful utterances, implying that speech is not stored in discrete cortical areas. Instead, the production of phonemes and syllables is thought to arise from a coordinated motor pattern involving multiple articulator representations.